There are an estimated 1.5 million manual wheelchair users in the United States. ~70% of manual wheelchair users report shoulder pain, which is directly linked to further disability including difficulty performing activities of daily living, decreased physical activity, and reduced quality of life. Overall, any loss of upper limb function due to pain adversely impacts the independence and mobility of manual wheelchair users. Subsequently, it is imperative to understand the mechanisms that contribute to upper limb pathology in manual wheelchair users so that appropriate interventions can be developed to prevent or minimize the effect of pain on function and reduce the risk of long-term upper extremity disability. Lack of variability in spatiotemporal characteristics of movements has been suggested to be a contributing factor to the development of overuse injuries. Although there has been considerable research on shoulder pain and manual wheelchair users, those studies have not explored motor variability. Further, the majority of factors (e.g. gender and injury level) contributing to shoulder pain are not modifiable;however, preliminary data suggest that propulsion variability is potentially modifiable with training. Therefore, the innovation of this proposal is to explore the variability profile of wheelchair propulsion and whether or not it correlates with shoulder pain in manual wheelchair users. The goals of this project are (1) to quantify the amount and time-evolving structure of kinetic, kinematic and temporal variability in wheelchair propulsion as a function of functional level (paraplegia vs. tetraplegia), and (2) to determine existence of an association between variability in propulsion mechanics and shoulder pain in manual wheelchair users. Our aims will be addressed using a cross-sectional design whereby manual wheelchair users (paraplegics and tetraplegics, with and without pain) will propel their own wheelchair while their propulsion mechanics (kinematic, kinetic, and temporal outcome measures) are recorded. We will measure the amount and time-evolving structure of their propulsion mechanics utilizing novel and standard non-linear dynamical measures. Shoulder pain will be assessed using self-report and functional examination. We hypothesize that there will be significantly greater kinematic, kinetic and temporal variability in higher functioning (paraplegic) individuals. We additionally hypothesize that kinematic, kinetic and temporal variability in wheelchair propulsion will be negatively associated with shoulder pain. The information gained from this project will provide vital information supporting a future prospective investigation in a larger sample of manual wheelchair users that would address whether motor variability is a predictor of should pain. . PUBLIC HEALTH RELEVANCE: This proposal has considerable importance for public health as the results will lead to a better understanding of correlates of shoulder pain in manual wheelchair users by taking the novel approach of examining motor variability in wheelchair propulsion mechanics. The project will introduce new tools and methodologies to the study of wheelchair propulsion and shoulder pain. Further, the results may be used to further determine the association between motor variability and shoulder pain in manual wheelchair users.